__exclusive__: .env.development.local

It serves as a that takes precedence over other environment files, but crucially, it is intended to remain only on your local machine [3jop]. Why is it Necessary?

.env.local .env.*.local

It is worth repeating: .env.development.local is . If you put production API keys in this file, your deployed application will not find them and will likely crash. Production environment variables should be injected directly through your cloud hosting provider's dashboard (such as Vercel, Netlify, AWS, or Heroku). .env.development.local